1. Field of the Invention
This invention relates to an optical sensor apparatus for detecting the passage of paper, provided in an image forming apparatus, such as a facsimile machine, a copy machine or the like.
2. Description of Related Art
In an image forming apparatus, such as a facsimile machine, a copy machine, or the like, plural sheets of plain paper are loaded in a cartridge or a tray for storing paper. When printed, each sheet of paper is fed sheet by sheet front the cartridge or the tray to a photosensitive drum, at which toner image is applied to the paper. Since respective processes and timings of image formation have to correspond to the position of the paper, such an image forming apparatus generally uses an optical sensor apparatus constituted of a plurality of optical sensors disposed at positions at which existence or passage of the paper is detected. In order to simplify control of the optical sensor device, those optical sensors are controlled by a control unit including a central processing unit. Output terminals of each optical sensor are connected to cables, respectively, which are connected to the control circuit. While light is being emitted from the light emitting device, if a sheet of paper passes between the light emitting device and the corresponding optical sensor, the control unit receives an output signal of a low voltage from the optical sensor, thereby detecting that the paper is passing by the optical sensor. If the output voltage remains in a high voltage, the control circuit detects that no paper passes by the optical sensor.
In an image forming apparatus having such an optical sensor apparatus constituted of a plurality of optical sensors, however, the number of cables increases as the number of the optical sensors increases. For example, in an image forming apparatus, such as a facsimile machine, using the optical sensor device of twenty sensors or above, a bundle of the cables becomes 5 to 10 mm in diameter, so that the cables are prone to prevent the image forming apparatus from being compact in size and light in weight.